1. Field of the Invention
The present invention relates to a radio resource allocation technique and a radio telecommunication technique and in particular to a technique effectively applicable to a radio telecommunication system performing radio telecommunications by reserving and using a set of plurality kinds of radio resources.
2. Description of the Related Art
Internet connections using mobile terminals have become popular and higher speed telecommunications are in demand. A mobile terminal connects itself to a base station by utilizing a radio resource, and the base station connects itself to another base station or to an external network such as the Internet so that a path is eventually established to a telecommunication correspondent. In order to enable a plurality of mobile terminals to connect to one base station by virtue of there being a limited number of radio resources, multiple access systems are used such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and Code Division Multiple Access (CDMA).
The TDMA allocates a short divided time slot to a user in the same frequency band, thereby multiplexing the users. The FDMA divides a frequency band into small sections and assigns a frequency band to each user. The CDMA allocates an orthogonal code to each user at the same time in the same frequency band, thereby multiplexing the users. Since the resources usable at a base station are limited, it cannot be fixed for a mobile terminal. Therefore, the method used is to allocate a spare resource to a mobile terminal at the time at which a telecommunication is carried out. This requires a control for allocating and disconnecting a resource effectively.
Effective allocation and disconnection of a radio resource is carried out by a scheduling process that is defined as determining the priority order of a process such as allocating a packet to a user of a channel with a high reception quality at a higher priority, for example.
Known representative scheduling methods include the Maximum Carrier-to-Interference power Ratio (Max CIR) method and the Proportional Fairness (PF) method, both of which are disclosed in reference non-patent document 1, for example.
Further, a transmission method suitable to a high speed telecommunication includes a multi-carrier transmission converting transmission information parallelly into plural pieces of data and parallelly transmitting the data by modulating the parallel pieces of data respectively for plural carriers of different frequencies within a transmission band. The multi-carrier transmission transmits data parallelly, enabling a high speed transmission. In this case, the symbol length of the multi-carrier modulation is longer than the original symbol length by an amount equivalent to the parallelization and therefore it is possible to reduce the influence of a multi-pass that is due to a delay of a reflection wave in a radio telecommunication. Also, it becomes robust against frequency selective fading because the band width per carrier is narrower in the frequency range. An example of one such multi-carrier transmission system is Orthogonal Frequency Division Multiplexing (OFDM) using orthogonal carriers. A parallel use of the OFDM system with TDMA or CDMA makes it possible to perform user multiplexing in a time zone or code zone in addition to carrying out a parallel transmission in the frequency direction and to use a radio resource effectively.
In the case of an access method for reserving a resource prior to carrying out a telecommunication, receiving the reservation result, and starting a transmission of data in a radio telecommunication, if there are a plurality of resources allowing a reservation, the amount of control information for notifying the allocated resource is increased.
As an example, in the case of a system in which a mobile terminal sends a resource reservation signal to abase station in an uplink transmission, then allocates a resource and notifies the mobile terminal of the result of allocation in a downlink channel, it is also possible to transmit data in a downlink direction and to control information containing the allocation result in the same channel for an effective utilization of the resource. Such a case results in the control information and downlink data sharing a predetermined amount of resources and the volume of downlink data allowed to be transmitted together being reduced if the amount of control information is large, thus generating the problem of decreasing the downlink throughput.
Reference patent document 1 has put forth a system performing a scheduling by using a three-dimensional resource comprising frequency, time, and code in which a head slot and allocated spatial range information are reported as notification information. The spatial information indicates a rectangular solid enclosed by the unit frequency band, unit time slot and unit code, a combination of a plurality of which is allocated when allocating using a form other than the rectangular solid. The amount of notification information proportionately increases with the number of solids and therefore, if the form of the spatial range information becomes complex, a large number of resources for carrying the control information are consumed, thus ushering in the problem of a decrease in downlink throughput. A decreased amount of transmitted information accompanies a decreased throughput, bringing about the risk of a delayed transmission of the information and the possibility of not satisfying a permissible delay in a real-time service; real-time service requires a strict requirement with regard to a delay, such as in the situation of a voice telecommunication (e.g., Voice over Internet Protocol (VoIP)) using a packet(s), a service that is predicted to be popular in the future.
Non-patent document 1: A. Jalali, R. Padovani, R. Pankaj, “Data Throughput of CDMA-HDR a High Efficiency-High Data Rate Personal Communication Wireless System”, VTC2000 Spring, May 2000
Patent document 1: Laid-Open Japanese Patent Application Publication No. 2005-117579